The present invention, in some embodiments thereof, relates to nanofabrication and, more particularly, but not exclusively, to an aligned nanoarray and method for fabricating an aligned nanoarray.
As the market for low-cost and/or high-performance/density micron- and nano-scale electronic and electromechanical integrated circuits increases, many new assembly techniques investigated and commercialized. At the same time, there has also been a continued interest in scaling to nanometer dimensions the size of individual devices within such integrated circuits. In this respect, nanostructures, and in particular elongated nanostructures such as nanowires and nanotubes, have the potential to facilitate a whole new generation of electronic devices. The small dimensions of electrically-conducting nanowires such as carbon nanotubes make them useful as nano-scale, vertically-connecting wires between circuit device layers as well as in-plane connecting wires between adjacent electrical pads. A major impediment to the emergence of this new generation is the ability to effectively grow and harvest nanowires and other nanostructures that have consistent characteristics.
There is also an interest exists in developing large area macroelectronic devices. The large area of such devices is not used to fit all of the electronic components, but rather because such systems must be physically large to realize improved performance and the active components of such systems must be distributed over the large area to realize a useful functionality. The incorporation of active devices over a large common substrate is driven by system performance, reliability, and cost factors, not necessarily by individual component performance. Such large area macroelectronic devices could revolutionize a variety of technology areas, ranging from civilian to military applications. Example applications for such devices include driving circuitry for active matrix liquid crystal displays (LCDs) and other types of matrix displays, smart libraries, credit cards, radio-frequency identification (RFID) tags for smart price and inventory tags, security screening/surveillance or highway traffic monitoring systems, large area sensor arrays, and the like.
Large-scale assembly of nanowire and nanotube elements presents a significant challenge facing their integration in electronic applications. Several efforts have been focused on tackling the problem of controlled assembly.
In one technique forces generated by electric fields are used to direct different populations of biofunctionalized nanowires to specific regions of a chip while providing registry between each individual nanowire and photolithographic features within the respective region. This approach can be applied to nanowires carrying different DNA sequences whereby sequential injections of the nanowires are synchronized with spatially confined electric-field profile that directs nanowire assembly [Morrow et al., “Programmed Assembly of DNA-Coated Nanowire Devices,” Science 323, 352-355 (2009)].
In another technique, nanochannel template guided methodology known as “grow-in-place” is employed. This methodology has been applied to single-wire four-point probe resistors and single-wire, top-gate SiNW unipolar accumulation metal oxide semiconductor field effect transistors [Shan, Y. and Fonash, S. J., “Self-Assembling Silicon Nanowires for Device Applications Using the Nanochannel-Guided ‘Grow-in-Place’ Approach,” ACS Nano 2, 429-435 (2008)]. In the grow-in-place methodology, an empty nanochannels present in a template guides the SiNW vapor-liquid-solid (VLS) growth. Depending on the details of the nanochannel length and the growth process, the resulting SiNWs can extrude form, or be confined within the template. The fabricated nanowires are always fixed by the guiding channels and only the exact number of nanowires needed is fabricated.
In another technique blown film extrusion is employed for the formation of nanocomposite films where the density and orientation of the nanowires and nanotubes are controlled within the film. The technique involves preparation of a homogeneous polymer suspension of nanowires or nanotubes, expansion of the polymer suspension, and transferring of the bubble film to substrates. [Yu et al., “Large-area blown bubble films of aligned nanowires and carbon nanotubes,” Nat. Nanotech. 2, 372 (2007)]
In another technique combines bottom-up nanowire assembly is combined with top-down microfabrication [Li et al., “Bottom-up assembly of large-area nanowire resonator arrays,” Nat. Nanotech. 3, 88, (2008)].
Other techniques involves assembly of nanowires by molecular forces within a solution, by electrostatic interactions which rely on inherent polarizability or a surface modification, by shear forces applied to surface carrying the nanowire, by magnetic fields applied to magnetic nanowires suspended within a solution, and by dielectrophoresis (to this end see a review by Wang, M. C. P. and Gates, B. D., entitled “Directed assembly of nanowires” and published on 2009 in Mater. Today 12, 34-46).